This invention relates to batteries, and, more particularly, to the negative current collector in a lithium ion battery cell.
A typical lithium ion battery cell includes a negative electrode, a positive electrode, a separator between the negative electrode and the positive electrode, and an electrolyte that saturates the separator and provides a lithium ion path between the negative electrode and the positive electrode. The negative electrode has a negative current collector contacting the negative electrode active material, and a positive current collector contacting the positive electrode active material. The negative electrode active material releases lithium ions upon discharging of the battery cell and absorbs lithium ions upon charging of the battery cell. The positive electrode active material reacts with lithium ions upon discharging of the battery cell and releases lithium ions upon charging of the battery cell. A lithium ion battery incorporates at least two, and typically a large number, of these cells within a container.
Each current collector provides an electrical current flow path between its respective electrode active material and a terminal, and thence to an external circuit. The current collector is a metal that is resistant to corrosion in the electrolyte, typically copper for the negative current collector and aluminum for the positive current collector. There must be good mechanical adhesion between each of the current collectors and its respective active material. A low electrical resistance at the interface between the current collector and the active material is also important, because the interface is in series with the current flow and imposes an interface impedance on the current flow.
Simultaneously achieving low electrical resistance and good mechanical adhesion between the current collector and the active anode material has been a problem for the case of the copper negative current collector. In one approach, a thin film is applied overlying the copper negative current collector to promote low electrical resistance and good adhesion. However, it is difficult and expensive in a production setting to apply the required thin coating in a precise, controllable, reproducible manner.
There is a need for an improved lithium-ion battery cell in which the interface between the negative current collector and the anode active material has both good adhesion and a low electrical resistance, and which is readily fabricated in production. The present invention fulfills this need, and further provides related advantages.